1. Field of the Invention
The present invention relates to a non-contacting electric potential sensor capable of measuring an electric potential of an object to be measured (a measurement object) based on the amount of electrical charge induced in a detecting electrode, and apparatuses, such as an image forming apparatus, using the electric potential sensor.
2. Description of the Related Background Art
Conventionally, there exists technology according to which a shutter disposed between a measurement object and a detecting electrode is driven to change the amount of electrical charge induced in the detecting electrode, and a surface electric potential of the measurement object is measured based on a change in the amount of electrical charge (see Solid-State Sensors and Actuators (The 7th International Conference) pp. 878–881). In such technology, the shutter is driven in a vacuum to achieve a low-voltage drive of the shutter, and driving noise is hence reduced by this low-voltage drive. The driving noise results from fields that are generated by a driver for driving the shutter and that reach the detecting electrode.
Further, there has been proposed another technology according to which a plurality of sets of a shutter and a detecting electrode are arranged, and each shutter, disposed between a measurement object and each detecting electrode, is driven to change the amount of electrical charge induced in the detecting electrode, such that a surface electric potential of the measurement object can be measured based on the change in the amount of electrical charge (see Japanese Patent Application Laid-Open No. 2000-147035 (its U.S. counterpart is U.S. Pat. No. 6,177,800)).
With those conventional technologies, however, the following phenomenon is likely to occur. When a shutter is driven using an electrostatic force, it is possible that electric fields generated by a shutter driver reach a detecting electrode. In such a case, driving noise due to those electric fields is likely to mix with an output signal from the detecting electrode. The driving noise disadvantageously affects an accurate sensing, and reduces the sensitivity of a potential sensor.